This invention relates to shoe manufacture and, particularly, to improvements in stiffening the shank region of the shoe which extends from the heel to the ball portions. Most shoes typically require some means to rigidify and stiffen the shank region. It has been substantially universal practice for many decades to stiffen the shank region by attaching a preformed steel, wood, or wood on fiber shank piece to the bottom of the insole of a lasted shoe assembly, before the outsole is attached so that after attachment of the outsole, the shank lies between the insole and outsole.
The use of preformed shanks such as steel shanks for this purpose has and still does present numerous problems. Because of the wide variety of shapes, sizes and styles of shoes, the manufacturer is required to maintain a very substantial inventory of preformed shanks. In order to insure an adequate supply of the various shanks which may be required at any time it is not uncommon for a manufacturer to overstock his inventory. Not infrequently, a manufacturer finds that a certain style or configuration of shank piece is no longer useable because of continually changing shoe styles.
It is common shoe industry practice to make a "case" of shoes at the same time in which the shoes in the case are of varying styles and sizes. A machine operator applying shanks to the bottoms of the insoles of the shoes in the case typically will have before him a wide variety of preformed shank pieces from which he must select the proper one to correspond to the particular shoe on which he is working. There is a reasonable chance that the operator may select the wrong shank piece for the particular shoe. Mismatching of the shank and shoe presents complications in the subsequent manufacturing steps of that shoe as well as further difficulties with the shoe after it has been completed and when it is worn. Moreover, even when the proper shank piece has been selected for a particular shoe, it is not uncommon for the shank piece to fail to fit the curve of the last and insole with the degree of conformity which is desired.
Also among the difficulties encountered with preformed steel shank pieces is that they must be placed on the insole in precisely the right location. They are typically attached to the insole at one or two specific locations, as by a nail, or adhesive, or a combination. Failure to properly place the shank often interferes with subsequent nailing operations, for example, when nailing the heel to the shoe. In general, the preformed shank pieces are difficult to place accurately and require a significant degree of operator skill.
Even when a shoe having a steel shank is properly assembled and manufactured, the steel shank may present difficultly when the shoe is worn. After a time, the steel shank piece may work its way loose from repetitive flexing and the shoe develops a squeak when worn. Remedial efforts to avoid a squeaky shoe have included taping of the steel shank piece in the hope that even if the shank does work loose, the taped shank piece will be less likely to rub against either or both of the insole and outsole. While this sometimes is effective, at least until the tape itself wears through, it does add to the cost and difficulty in manufacture of the shoe.
A further difficulty sometimes encountered with preformed steel shank shoes is that the steel shank can be felt by the wearer. Efforts to overcome this have included the addition of a sheet or layer of cushioning material (sometimes called a "tuck") interposed between the shank and the insole. Here, again this adds to the cost and only further complicates the manufacturing procedure.